Heretofore it has been known to utilize sealing glands for various types of pipe joint constructions. These sealing glands which are customarily made from elastomeric material initially function very well in both low pressure environments, such as 15-20 psi, and in high pressure environments of 50 or more psi if care is taken to ensure close tolerances and smooth surfaces through lining of the jointing area.
However, problems occur when the elastomeric material ages and takes a permanent set and when slight or major separation of the adjoining conduits occurs over time because of settlement, vibration, tensile forces and other disturbances. When separation occurs the gasket is backed out in the joint area. Frequently, the spigot end has a slight taper and this may accelerate the separation. If the gasket has taken a compression set or the adjoining conduits have separated significantly, the fluid begins to leak at the joint. In cases when the conduit is lain in or supported by a medium such as soil, the leakage wets the soil in the joint area, dissolves it, and transports it away. This creates a washout situation which further exacerbates the disjointing condition, causing increased leakage and more severe disjointing or uncoupling.
A different type of disadvantage results when surface roughness or discontinuities of the interior surface of the conduit occasionally occur in several joints out of a number of joints and permit leakage of a small amount of material. For example, when used as a water line or sewerage line and the line is tested with air or water, the joint may fail or be considered marginal, when concrete pipe is used as the conduit material as compared to the smoother walls obtained for extruded plastic pipe.
Historically, when the conduit is pipe and the fluid is water, repeated occurrences have shown that even minor leakage can wreak havoc over long periods of time. When the intended use is a water line, sewerage line or disposal line, even minor leakage cannot be tolerated. While simple compression type gaskets may be watertight for several years, the invention of the present invention is intended to remain absolutely watertight for 20-60 years, with the ability to continue performing even with differential settlement of the conduit. The need for this reliability will be appreciated when it is considered that many conduits are placed under pavements, sidewalks, parking lots, and buildings where repair of the conduits is extremely expensive and disruptive.